1. Field of the Invention
The present invention relates to display devices, and in particular, display devices for ergonomic helmet-mounted sights.
2. Discussion of the Background
In helmet-mounted sights, a collimated light image is observed superposed on the view corresponding to the surroundings. A collimating optical system is used to reflect a light image, for example, an image corresponding to the date. The sight avoids excessive exertion of the eye of the observer and therefore provides great visual comfort. In conventional head-up use on board aircraft, the light image is reflected by a combination optical system to the observer. The radiation coming from the surroundings passes through this optical system. Thus the observer sees, in superposition on the surroundings, the collimated light image corresponding, for example, to a synthetic image which shows aerial navigation data.
In published French patent application No. 2,593,932, a display device is disclosed having a collimation and combination optical unit including a holographic spherical mirror used on the axis for observing, from the center of this mirror, a collimated light image, and a semitransparent mirror inclined on said axis corresponding to the normal direction of view for the observation of the superposed collimated image in the surroundings and a generator of the light image to be collimated whose radiation reaches the semitransparent mirror. The semitransparent mirror reflects the radiation to the spherical mirror, on the concave side thereof, when the radiation is reflected to the semitransparent mirror which transmits it in the direction of the observer. This device is characterized in that the radiation of the light images first passes through the spherical mirror on which it falls incident, on the convex side thereof, with an incidence outside of the incidence range for which the mirror is designed to selectively reflect the radiation passing through this spherical mirror in the direction of the semitransparent mirror. The optical unit is placed in a transparent medium forming a plate with parallel faces which constitute a stigmatic system for infinity.
According to 2,593,932, more particularly intended for the production of ergonomic helmet-mounted sights, the image generator and the observation point are placed on the same side relative to the optical unit, and the unit is completed by a reflecting mirror to reflect the radiation from the generator along its optical axis to the convex face of the spherical mirror.